California’s greenhouse gas emissions declined by about 1% in 2017, with a continued shift toward renewable electricity keeping the state ahead of schedule in meeting its 2020 climate target, according to a report released Monday by air quality regulators.

The state Air Resources Board inventory found 2017 was the first year since the state began tracking planet-warming emissions that electricity generated from solar, wind, hydroelectric and other renewable sources surpassed what was generated by fossil fuels. Clean power provided 52% of the electricity California used in 2017, according to the report.

The gains came so heavily from the electricity, environmental policy experts say, that the sector is making up for more lackluster areas of the economy, such as transportation and industry. Emissions in those sectors are flat or even ticking upward, despite California’s nation-leading climate policies. The 9% decline in greenhouse gases from electricity generation was the largest of any sector tracked in the report.

“These zero-GHG emissions fuels are supplanting a continually larger part of the petroleum and coal market,” said Dave Clegern, an Air Resources Board spokesman. “And those are good trends that will see us through for some time.”

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But the news wasn’t so good for the climate in other sectors, including industry, where emissions remained essentially flat.

Transportation pollution, which has been creeping stubbornly upward in recent years, continued to climb — though at a slower rate of 1% annually. The transportation sector remains California’s largest source of greenhouse gas emissions, accounting for about 40% of the state’s total.

Overall, the state released the equivalent of 424 million metric tons of carbon dioxide in 2017, marking the second year in a row that planet-warming pollution was below the limit of 431 million metric tons the state must meet by 2020. Reductions in 2017 slowed down over the year before — with greenhouse gas emissions falling 1.2% in 2017 compared to 2.8% in 2016. That won’t be enough for the state to reach its more ambitious goal to slash greenhouse gas emissions an additional 40% by 2030.

“The pace has got to pick up significantly in the coming years if we’re going to get to meet the 2030 goal,” said Danny Cullenward, policy director at climate change think tank Near Zero and a researcher at Stanford Law School. “It has to be about 2-1/2 times what we saw in this year’s data.”

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It’s a similar dynamic to last year, when regulators announced the state had hit its goal of reducing greenhouse gas emissions below 1990 levels four years early.

“Once again, for another year running, nearly everything that’s positive in the headline number is from the electricity sector,” Cullenward said. “No other sector is making major contributions, and a couple are headed in the opposite direction.”

State officials, for their part, heralded the latest numbers as more evidence that you can cut pollution while growing the economy. California’s GDP increased by 3.6% between 2016 and 2017.

“California is proving that smart climate policies are good for our economy and good for the planet,” Gov. Gavin Newsom said in a statement. “As the Trump Administration attempts to obliterate national climate protections, California will continue advancing the cause of American climate leadership.”

Air quality officials said they hoped other areas of the economy would follow in the footsteps of power generation, showing more dramatic decreases as the state’s climate policies phase in over time. The inventory does not capture wildfire emissions, which almost certainly increased with the series of large wildfires that devastated parts of California over the past couple of years.

One of California’s biggest challenges is cutting carbon pollution from cars, trucks and other transportation sources at a time when state officials are battling the Trump administration over its plan to weaken fuel economy standards and revoke California’s power to set its own, stricter rules. Those planned rollbacks — combined with increased driving, a consumer trend toward roomier, less-fuel-efficient SUVs and a slower-than-anticipated switch to electric models — will only make it more difficult to reduce those emissions.

Dave Edwards, an assistant division chief at the Air Resources Board who oversees the greenhouse gas emissions inventory, said the 1% increase in transportation pollution in 2017 is a notable improvement from a few years ago, when the sector was growing by about 3% or 4% annually.

“So something externally is causing the amount of emissions to not grow as quickly,” he said. “We are hoping it’s our policies,” but added: “We don’t speculate.”

Still, Jackson sees reasons for hope. He pointed to other state data showing gasoline and diesel sales were down in 2018 relative to 2017, which could be an early sign that car and truck emissions may have peaked.

Still, he cautioned against placing too much significance in year-over-year changes in greenhouse gas emissions because they can be heavily influenced by weather,including more rain in 2017that increased the state’s use of hydroelectric power.

Just as it would be a mistake to declare success based on one big hydroelectric year, he said, “it would be a mistake to see an increase in electricity emissions next year then be in a panic that California’s programs are failing.”

“The big picture here is that a large economy is still bending down its emissions without sacrificing its economic growth, and that’s further proof that those are not in conflict,” Jackson said. “Still, the numbers are sobering in terms of the enormity of the challenge that lies ahead.”

Tony Barboza is a reporter who covers air quality and the environment with a focus on Southern California. He has been on staff at the Los Angeles Times since 2006, is a graduate of Pomona College and completed a Ted Scripps Fellowship in Environmental Journalism at the University of Colorado.